Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
  • G01S19/05—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing aiding data
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
  • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/53—Determining attitude
  • G01S19/54—Determining attitude using carrier phase measurements; using long or short baseline interferometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/13—Receivers
  • G01S19/22—Multipath-related issues

Definitions

• Embodiments are generally related to direction finding systems. Embodiments are also related to a method and system for determining north In target locator systems. Embodiments are additionally related to a single receiver GPS pointing vector sensing system.
• GPS navigation systems include a consteliation of satelSites each of which provides a coded signal which may be picked up by radio receivers on the surface of the earth. Separate coded signals from a set of satellites may be processed by a receiver system for use in determining location as defined by latitude and longitude based on the code carried by the signals. The operation of GPS systems in determining location based on coded signals received from satellites reflects the conventional functioning of such systems.
• the signals generated by GPS satellites may be used in other ways and in particular the carrier phase of the signals may be used in certain surveying applications.
• a pair of stationary antenna/receiver combinations may be located at the ends of a baseline (whose length is required to be determined) and, based on the i observed relative phase of the GPS carrier signal from satellites at known positions, determine the orientation of the antenna pair relative to an earth reference.
• Digital magnetic compasses are currently used in handheld target systems to determine orientation relative to north. These devices may be easily influenced by local fields due to geological formations, metal vehicles and even equipment worn by the user. There is generally no indication when these devices are compromised leading to incorrect targeting solutions. GPS solutions are generally discounted as they can be influenced by muitipath effects or jamming.
• It is another aspect of the present invention to provide a GPS system for determining north in a target locator system with two antennas includes two stationary GPS antennas separated by less than half a wavelength.
• a single receiver is also included, and is used to determine the pointing vector of the system,
• a system and method of determining a pointing vector using two GPS antennas and a single GPS receiver is disclosed- Two stationary GPS antennas, with a separation preferably less than half of a wavelength ( ⁇ 100mm) may use a singie receiver to determine the pointing vector of the system. Incorporation of a three axis angular rate measurement allows pointing determination during system rotation.
• the present invention provides the ability to sense muiiipath and jamming, potentially alerting the user that the measurement may not be reliable.
• FIG. 1 illustrates a schematic diagram of a GPS system showing an orientation of two antennas with respect to a satellite, in accordance with the disclosed embodiments
• FIG. 2 illustrates a schematic diagram of the system depicted in FIG. 1 with the antenna configuration rotated 90 degrees relative to the satellite, in accordance with the disclosed embodiments;
• FIG. 3 illustrates a block diagram an of first antenna being scaled by a sinusoidal waveform, in accordance with the disclosed embodiments
• FIG. 4 illustrates a graph of carrier amplitude relative to antenna output as a function of alpha, in accordance with the disclosed embodiments
• FIG. 5 illustrates a graph of carrier phase relative to antenna output as a function of alpha, in accordance with the disclosed embodiments
• FIG. 8 illustrates a block diagram of the processor depicted in FIG. 3 utilized for determining a pointing vector directly from measurements of a carrier phase, In accordance with the disclosed embodiments; and [0023] FIG. 7 illustrates a graph of the scale from predicted amplitude to measured amplitude, in accordance with the disclosed embodiments.
• FIG. 1 a schematic diagram of a GPS system 100 showing an orientation of first and second antennas 102 and 104 with respect to a satellite.
• the orientation can be for example, the satellite and the first and second antennas 102 and 104 are in same plane.
• the transmission direction 106 of the satellite is indicated with the dotted arrow.
• the first antenna 102 and second antenna 104 have their phase centers 108 aligned to the vector Indicated with the solid arrow.
• the carrier signal 10 is illustrated by the sine wave.
• the carrier signal 1 0 has a phase of zero at the first antenna 102.
• the phase at the second antenna 104 can also be calculated.
• the GPS carrier frequency is nominally 1.57542 GHz corresponding to with a wavelength of 190.3 millimeters. If the first and second antennas 102 and 104 are separated by fifty four millimeters, the phase 112 on the carrier wave 110 on the second antenna 104 relative to the first antenna 102 is calculated as
• the antenna configuration of FIG. 1 is rotated ninety degrees relative to the satellite.
• the first and second antennas 102 and 104 receive the same carrier phase resulting in a zero degree phase difference. This illustrates the dependency on phase difference with orientation on the horizontal plane.
• phase difference observed between the two antennas for each of the satellites in degrees for this example can be determined as
• Phase difference ⁇ 102*eos ⁇ where 0 is the angie between the vector defined by the phase centers 108 and the vector pointing to the transmission direction 106 of the satellite.
• Equation (2) where ⁇ is the maximum phase difference determined by the antenna separation of hundred and two degrees.
• the vector to the satellite defined by ⁇ ⁇ ! y n , 3 ⁇ 4 are indicated as time varying as the satellites are in motion.
• n n represents the noise on the carrier phase measurement from the GPS receiver.
• xb, yb and zb there are three unknowns in the equation (2), xb, yb and zb. In a noise free measurement, these values may be determined from three sateliite measurements to satisfy the three equations, three unknown criteria for the unique solution. In the presence of noise, the three unknowns can be solved by taking many measurements, either using more than three satellites or using many measurements through time.
• the GPS position solution requires a minimum of four satellites and generally, more than four satellites are available adding more measurements to the least squares fit.
• the problem is amenable to recursive least square solution for a static system or may be incorporated into a Ka!man estimator for a dynamic system with the addition of inertia! sensors to predict rotation of the Xb, y and z b vector components.
• One embodiment of this disclosure is the method used to sense the satellite dependent carrier phase shift at the two receiving antennas using a single receiver,
• the antenna outputs are scaled by time varying gains and summed in order to generate a carrier phase modulation that is dependent on satellite orientation.
• the first antenna 102 being scaled by a sinusoidal waveform 118 with a minimum amplitude of zero and peak amplitude of one is shown by utilizing a scaler 114, typicaily implemented with a variable gain amplifier or variable attenuator.
• the apparatus 300 can be utilized for determining a pointing vector 130.
• the second antenna 104 is scaled by another sinusoidal waveform 120 with identical frequency but one eighty degrees out of phase by utilizing another scaler 116.
• the scaled antenna outputs 121 and 1 9 are summed and fed into a GPS receiver 124 antenna Input by utilizing a summe 122.
• White scaling with a sinusoid over a range of zero to one is used In this example, other waveforms and amplitudes may be used to the same effect.
• the sinusoid offers the greatest amplitude swing with the smallest resultant jerk, minimizing potential issues in receiver carrier tracking loop.
• the GPS receiver 124 processes the summed antenna signal 123 using standard GPS receiver software to generate a satellite almanac 132 that allows prediction of satellite position, provide raw carrier phase measurements 134 and determine the GPS receiver location 136. These standard data outputs are input to a processor 26 along with the measured modulation 120 and the measured inertial rotation rates 127 provided by the inertia! measurement system for example three axis gyroscope 128.
• the raw carrier phase measurements include a measure of the phase modulation induced by the time varying summatio of the two antenna signals.
• the processor 126 determines the pointing vector 130 based on the signals from GPS receiver 24 and three axis gyroscope 128.
• the second antenna output can be equiva!entiy expressed as: ssn ⁇ COS(Y) sin(w c t)+ (1-a) sin ⁇ v) cos(u> c t) Equation (7)
• FiG. 4 illustrate a graph 400 showing the variation of the carrier amplitude as a function of alpha parametric with gamma
• FiG, 5 Illustrate a graph 500 showing the variation of carrier phase as a function of alpha parametric with gamma.
• the operating point selected for the exampie was a maximum phase delta of 102 degree (1.78 radians), resulting in a periodic amplitude loss on the carrier varying from 1 ,0x to 0,82x.
• the optimum operating point is a trade between maximizing the resultant phase modulation versus the impact of the amplitude modulation on the ability of the receiver to track iower signal levels, it may also be desirable to use lower gammas (smaller antenna separation) so that the phase response shown in FIG. 5 stays somewhat linear in order to preserve the sinusoidal modulation shape.
• the selected gamma of 1.78 radians has a slight non-linearity in phase response as if varies from 0 to 1.78 radians.
• FIG. 6 a block diagram of the processor 126 depicted In FfG. 3, utilized for determining the pointing vector 130 directly from a carrier phase measurement 134 is shown.
• the satellite almanac 132 and receiver position 603 are given as input to the compute satellite position module 602.
• the compute satellite position module 602 determines the time varying range to each satellite and the time varying unit vectors pointing to each satellite in the local East-North-Up (ENU) reference frame.
• the range is expressed in terms of phase based on the wavelength and represented as Doppier phase rate 607.
• the time varying unit vectors are represented as satellite ENU unit vectors 605.
• the carrier phase measurement 134 is subtracted from the Doppier phase rate 607 by utilizing a subtrator 604.
• the resultant phase measurement 61 1 includes a residual phase rate and low frequency phase variation as well as the desired phase modulation.
• a rolling average equal to the period of the carrier phase modulation is computed and subtracted from the phase measurement in order to remove the residual phase errors and preserve phase modulation information.
• a rolling one second average signal 613 obtained from a one second average module 610, is subtracted from the resultant phase measurement 6 1 by utilizing a subtrator 606. This eliminates low frequency variation and converts any residual phase rate into a constant offset.
• the antenna modulation signal 120 is given as input to a pointing vector estimator 608,
• the pointing vector estimator 608 may be a Kaiman estimator.
• the gyroscope Input is integrated to create a Direction Cosine Matrix (DC ) corresponding to the rotation of the system since the previous estimator iteration. This is used by the estimator to predict the pointing vector 130 for the next estimator iteration,
• DC Direction Cosine Matrix
• a Kaiman estimator is provided here as the preferred implementation for the pointing vector estimator 608, other estimator im lementations are possible.
• the state for the estimator is defined as:
• Earth referenced unit vectors for satellites 1 through n are caicuiated from the satellite almanac 132 provided by the GPS receiver 24:
• Equation 15 For a 1 Hz phase modulation, the gain on antenna 1 , a, is defined as a k ⁇ 0.5 sin (lm k ) + 0.5 Equation (15)
• the measurement prediction is the predicted carrier pha xpressed in meters as determined by:
• b ⁇ l ⁇ a t )sm(f k ) Equation
• the linearized measurement prediction is determined from:
• Q is zero for stationary operation.
• Q must be set based on the rotational motion anticipated.
• R is a diagonal matrix with the values in the diagonal set to the set to the variance of the carrier phase noise, high pass filtered with a 1 Hz cutoff frequency
• the magnitude of the predicted carrier phase modulation and the measured carrier phase modulation ideally match at steady state.
• the magnitude of the difference between measurement and prediction can be used as a measure of the accuracy of the solution. Satellite signals with significant difference between prediction and measurement are likely impacted by mu!tipath or jamming signals and can be selectively dropped from the solution until a minimum accuracy as determined by the remaining difference has been achieved.

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• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Computer Networks & Wireless Communication (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Position Fixing By Use Of Radio Waves (AREA)

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• 2012
  • 2012-08-16 PL PL12825888T patent/PL2748634T3/pl unknown
  • 2012-08-16 WO PCT/US2012/051056 patent/WO2013028443A1/en active Application Filing
  • 2012-08-16 EP EP12825888.6A patent/EP2748634B1/en not_active Not-in-force
  • 2012-08-16 US US13/883,376 patent/US9778365B2/en active Active

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